The present invention relates to a mirror lighting unit for a rod-shaped lamp, especially a fluorescent tube, having longitudinal mirrors extending on both sides parallel to the lamp. The unit also has louvre vanes arranged transverse thereto underneath the lamp and adjusted relative to the lamp with the base of their double-parabola-shaped cross-section. All along their length the louvre vanes have a hood-shaped cover with reflecting surfaces on the base side of their cross-section. With this the line of intersection of the cover with a plane extending perpendicular to the longitudinal axis of the lamp has a concave curvature symmetrical in relation to the longitudinal axis of the lamp.
A mirror lighting unit of this type is disclosed, for example, in the German reference DE 3,112,210 C2. Here, the hood-shaped cover consists of a silvered injection-moulded part, which is mounted with its base side onto the louvre vane and, starting from a central zone, extends along the louvre vane, increasing in height towards the vane rim. With such a hood-shaped cover it is certainly possible to avoid undesirable reflections at this cover, but the expense required for this is substantial.
Reflecting covers of louvre vanes are known, for example from the British reference GB Patent 814,354, which are also mounted at the base sides on the louvre vanes, and can have a plane, triangular or arch-shaped cross-section. For mirror lighting units requiring a luminous density less than or equal to 200cd/m.sup.2, the so-called "condition", for angles of emission.gamma. greater than or equal to 50.degree., it is not possible to guarantee this demand with certainty in every case. In this case, the base-side reflecting cover of the louvre vanes cannot prevent the image of the lamp emerging from the unit by virtue of multiple reflections at an angle of .gamma. greater than 50.degree., that is from causing the lamp to flash. In this connection, sections of the cover extending along the louvre vanes are especially critical in the rim zone of the louvre vanes, whereas in the central zone a plane cover is often required.
In order to eliminate the effect of these rim zones it is therefore necessary, as is the case for the mirror lighting unit according to the first-named reference, to raise the base-side reflecting cover in the rim zones of the louvre vane above the height of the latter's base.